This invention relates to an ignition timing control system for an internal combustion engine.
The ignition timing of internal combustion engines is set so as to maximize the efficiency of the engine with respect to the mode of operation thereof. It is generally desirable to set the ignition timing so that the particular internal combustion engine approaches a minimum advance for the best torque which may be abbreviated to "MBT" as close as possible within the range in which knocking is not caused in the engine. However, ignition timing control systems previously equipped on internal combustion engines have been, in many cases, of the mechanical type and the ignition advance angle characteristic thereof have not been stable with respect to deviations of dimensions and secular changes of components involved. Therefore, the ignition timing has been actually set to retard the timing somewhat behind the optimum ignition timing point which provides the most desirable advance angle characteristic in order to prevent the occurrence of knocking. In such a case, the engine efficiency is deteriorated. Furthermore, even if ignition timing control systems which are free from both deviations of their dimensions and secular changes, as described above, would be employed, knocking occurring in an associated internal combustion engine depends upon the inlet air temperature and the inlet humidity of the engine and further upon the air fuel ratio thereof etc. Accordingly, if the ignition timing could be set so as not to cause knocking in the engine in some mode of operation, there might be a fear that knocking would be caused in the engine in another mode of operation.
Therefore, by sensing knocking and controlling the ignition timing to retard same upon the occurrence of knocking, the ignition timing can be adjusted so that knocking is scarcely caused even though an error would occur in the ignition advance angle characteristics due to the deviations as described above of the mechanical apparatus and differences between the modes of operation. Knocking can be sensed according to any method of measuring a pressure within the combustion chamber of internal combustion engines, the acceleration of vibrations of the engines, sound generated in the engines, etc. In actual motor vehicles, the method of measuring the acceleration of vibration of an associated engine is most practical in view of a position where an acceleration sensor involved is mounted, the processing of signals, etc. As the method of measuring the acceleration is responsive to a knock singal and simultaneously to vibrational noise signals, it has been necessary to select the knock signal from among the vibrational noise signals.
Accordingly, it is an object of the present invention to provide a new and improved ignition timing control system for an internal combustion engine for determining the optimum ignition timing by sensing a knock signal from an output from an acceleration sensor for sensing the acceleration of a vibration of an associated internal combustion engine without various noise components interfering with the knock signal, and controlling the ignition timing in accordance with the sensed knock signal.